1. Field of the Invention
This invention relates to an ion injection device, and more particularly to improved wafer-positioning and transfer devices being applicable to the ion injection device.
2. Description of the Related Art
When a semiconductor wafer is treated by an ion injection device, it is necessary to determine the direction of a wafer (i.e., to position the orientation flat of the wafer) since the crystal of the wafer has polarity, and also to align the wafer so as to accurately fix it to the device.
Thus, in the conventional method, a wafer is once placed on the rotatable holding table of a wafer-positioning device located in the air, and held thereon by vacuum sucking. Thereafter, the direction of the wafer and the center position of the same are detected with the holding table rotated, thereby adjusting the position of the wafer. The holding table with the wafer is moved into a vacuum treatment chamber through a load lock chamber, thereby transferring the wafer onto a holding unit contained in the vacuum chamber.
In general, to enhance the efficiency of the system, it is more effective to detect the direction of the wafer under vacuum than in the air.
Actually, however, it is very difficult to locate the positioning device in vacuum atmosphere, because vacuum sucking cannot be utilized in the vacuum atmosphere to hold the wafer on the holding table. If a rubber member or the like having a high friction factor is used to prevent slippage of the wafer, dirt of the rubber member may be adhered to the wafer, or chemical contamination may occur. Further, if the rotational speed or the rotational acceleration of the holding table is high, and/or if the vibration of the same is high, the wafer may slip from its correct position, and may drop therefrom and be broken.
Moreover, in the ion injection treatment device, the wafer is transferred by a transfer arm between a platen on an injection disk, contained in the vacuum treatment chamber add the load lock chamber.
Vacuum sucking cannot be utilized in the transfer arm as in the holding table, so that the wafer has been prevented from slipping, by means of a rubber member of a high friction factor mounted on the arm, or from dropping, by means of an abutment plate or so surrounding the wafer.
However, where a rubber member of a high friction factor is used, dirt of the member may be adhered to the wafer, or dust may be caused from rubber itself, or chemical contamination may occur. Further, when the vibration and/or acceleration of the transfer arm is high, the wafer may slip from its correct position, and may drop from the arm.
On the other hand, where an abutment plate is provided for the transfer arm, a gap may be caused between the plate and wafer, whereby the wafer is moved, and hence may cause dust or be broken, Also, since the tip portion of the arm is thick, the accessibility of the arm to a wafer carrier containing many wafers at a narrow pitch is inevitably deteriorated.